The present invention relates to a method of forming a hollow pole projecting on a plate such as a metal plate to which various components are to be attached or which is to support a rotating member, and a method of forming heat dissipating fins by utilizing the aforementioned hollow poles in order to dissipate heat away from electronic components generating said heat in an effective manner by providing the heat dissipating fins in the vicinity of the electronic components.
In order to axially support a rotating part or axially affix other parts to a plate such as a metal plate, a hole is bored in the plate and a specially manufactured axial member is then passed through the hole. The axial member is then fixed using end fixing means or using a screw.
However, the number of components required when an axial member is separately made and fixed to a plate is large, as is the number of manufacturing steps, and high costs are therefore inevitable. Because of this, in Japanese Patent Laid-open Publication No. Hei. 6-26737, the present applicant proposed a method of integrally forming a cylindrical projection by utilizing plastic processing technology, which was extremely useful in practical terms.
FIG. 9 and FIG. 10 are views showing a method of forming a cylindrical projection at a plate proposed in the related art, where FIG. 9 is a view showing a method of forming a cylindrical projection having a bottom in the plate. First, in a first press step #10, a press tool 401 that is a circular column formed with a flat end surface is pushed against one surface of a plate 400 comprising a metal plate of a metal having plasticity such as iron or aluminum so as to form a hole 102 at the one side and a projection 403 at the other side.
Next, in a flat press step #11, the end surface of a columnar flat press tool 404 of an external diameter greater than the external diameter of the projection 403 is brought into contact with the side of the opening of the hole 402 and pressed. As a result, the metal of the pressed portion moves towards a central section 405 of the hole 402 that provides no resistance and is also moved to the projection 403 so that the projection 403 is made to project further.
In a second press step #12, the plate 400 that has undergone the flat press step #11 is again pressed by the press tool 401 from the side of the opening and the height of the projection is further increased so as to form a cylindrical projection 406 at the plate 400. The height of the cylindrical projection 406 is then two times a thickness t1 of the plate 400 or more.
FIG. 10 is a view showing a method of forming a cylindrical projection that penetrates the plate from one side to the other. Namely, up to the flat press step #11, the steps shown in FIG. 9 are gone through. Thereafter, a boring step is provided. Here, a boring tool 407 having a stem portion of a small diameter is inserted through the hole 402 and punching is carried out so as to bore a thruhole 408. Next, in a burring step #14, a burring tool 409 with a tapered front end and an external diameter that is the same as the diameter of the press tool 401 is inserted from the hole 402 and passed through while broadening out the thruhole 408 so as to form a cylindrical projection 410 having a height L02. In the method shown in FIG. 10 a height L02 of the cylindrical projection 410 is also formed to be at least twice the thickness t1 of the plate 400.
In the methods of forming a cylindrical projection at a plate described above, the cylindrical projection 406 are integrally formed at the sheet 400. Costs are therefore reduced and cylindrical projection having a height of twice the thickness of the plate 400 or more can be formed at the plate 400. There is a limit on making the cylindrical projection substantially larger with respect to the thickness t1 of the plate 400 in that the direction of the movement of the metal due to pressing by the flat press tool 404 is dispersed. There are also cases where a thick projection is required but there are limits when the thickness is increased in the related axial part forming method for the reasons state above.
As the present invention sets out to resolve the aforementioned problems of the related forming methods, it is the object of the present invention to provide a method of forming a cylindrical projection, which is substantially a hollow pole, in a plate where the hollow pole can be made substantially higher with respect to the thickness of the plate or where the thickness of the hollow pole is made thicker.
It is also a further object of the present invention to provide a method of easily and cheaply manufacturing a heatsink with superior heat dissipating effects by forming one or more heat dissipating fins utilizing the aforementioned hollow pole, and to provide a heatsink thereof.
In order to achieve the aforementioned object, according to the present invention, there is provided a method of forming a hollow pole projecting from a metal plate by plastic deformation and comprising the steps of: (a) pressing the plate from one surface of the plate using a press tool so as to form a hole on the one surface and a projection on the other surface thereof; (b) moving metal of the plate around said projection towards interior of said hole so as to gather the metal into a periphery of an opening of said hole using a tapered tool; (c) pressing said periphery of said hole using a flat press tool which is greater than said projection in an external diameter so as to move the metal gathered by said tapered tool further towards the interior of said hole and to increase a height of said projection; and (d) inserting said press tool into said hole while pressing the interior of said hole so as to increase further the height of said projection and to form the hollow pole. The projection can therefore be made substantially higher with respect to the thickness of the plate or the thickness of the hollow pole can be made thicker. Further, a heatsink utilizing the hollow poles as superior heat dissipating fins can be manufactured easily and cheaply.